/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     |
    \\  /    A nd           | www.openfoam.com
     \\/     M anipulation  |
-------------------------------------------------------------------------------
    Copyright (C) 2011-2017 OpenFOAM Foundation
-------------------------------------------------------------------------------
License
    This file is part of OpenFOAM.

    OpenFOAM is free software: you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    for more details.

    You should have received a copy of the GNU General Public License
    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.

\*---------------------------------------------------------------------------*/

#include "BrownianMotionForce.H"
#include "mathematicalConstants.H"
#include "fundamentalConstants.H"
#include "demandDrivenData.H"
#include "turbulenceModel.H"

using namespace Foam::constant;

// * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * * //

template<class CloudType>
Foam::scalar Foam::BrownianMotionForce<CloudType>::erfInv(const scalar y) const
{
    const scalar a = 0.147;
    scalar k = 2.0/(mathematical::pi*a) +  0.5*log(1.0 - y*y);
    scalar h = log(1.0 - y*y)/a;
    scalar x = sqrt(-k + sqrt(k*k - h));

    if (y < 0.0)
    {
        return -x;
    }
    else
    {
        return x;
    }
}


template<class CloudType>
Foam::tmp<Foam::volScalarField>
Foam::BrownianMotionForce<CloudType>::kModel() const
{
    const objectRegistry& obr = this->owner().mesh();
    const word turbName =
        IOobject::groupName
        (
            turbulenceModel::propertiesName,
            this->owner().U().group()
        );

    const turbulenceModel* turb = obr.findObject<turbulenceModel>(turbName);

    if (turb)
    {
        return turb->k();
    }

    FatalErrorInFunction
        << "Turbulence model not found in mesh database" << nl
        << "Database objects include: " << obr.sortedToc()
        << abort(FatalError);

    return nullptr;
}


// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //

template<class CloudType>
Foam::BrownianMotionForce<CloudType>::BrownianMotionForce
(
    CloudType& owner,
    const fvMesh& mesh,
    const dictionary& dict
)
:
    ParticleForce<CloudType>(owner, mesh, dict, typeName, true),
    rndGen_(owner.rndGen()),
    lambda_(this->coeffs().getScalar("lambda")),
    turbulence_(this->coeffs().getBool("turbulence")),
    kPtr_(nullptr),
    ownK_(false)
{}


template<class CloudType>
Foam::BrownianMotionForce<CloudType>::BrownianMotionForce
(
    const BrownianMotionForce& bmf
)
:
    ParticleForce<CloudType>(bmf),
    rndGen_(bmf.rndGen_),
    lambda_(bmf.lambda_),
    turbulence_(bmf.turbulence_),
    kPtr_(nullptr),
    ownK_(false)
{}


// * * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * //

template<class CloudType>
Foam::BrownianMotionForce<CloudType>::~BrownianMotionForce()
{}


// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //

template<class CloudType>
void Foam::BrownianMotionForce<CloudType>::cacheFields(const bool store)
{
    if (turbulence_)
    {
        if (store)
        {
            tmp<volScalarField> tk = kModel();
            if (tk.isTmp())
            {
                kPtr_ = tk.ptr();
                ownK_ = true;
            }
            else
            {
                kPtr_ = &tk();
                ownK_ = false;
            }
        }
        else
        {
            if (ownK_ && kPtr_)
            {
                deleteDemandDrivenData(kPtr_);
                ownK_ = false;
            }
        }
    }
}


template<class CloudType>
Foam::forceSuSp Foam::BrownianMotionForce<CloudType>::calcCoupled
(
    const typename CloudType::parcelType& p,
    const typename CloudType::parcelType::trackingData& td,
    const scalar dt,
    const scalar mass,
    const scalar Re,
    const scalar muc
) const
{
    forceSuSp value(Zero);

    const scalar dp = p.d();
    const scalar Tc = td.Tc();

    const scalar alpha = 2.0*lambda_/dp;
    const scalar cc = 1.0 + alpha*(1.257 + 0.4*exp(-1.1/alpha));

    // Boltzmann constant
    const scalar kb = physicoChemical::k.value();

    scalar f = 0;
    if (turbulence_)
    {
        const label celli = p.cell();
        const volScalarField& k = *kPtr_;
        const scalar kc = k[celli];
        const scalar Dp = kb*Tc*cc/(3*mathematical::pi*muc*dp);
        f = sqrt(2.0*sqr(kc)*sqr(Tc)/(Dp*dt));
    }
    else
    {
        const scalar s0 =
            216*muc*kb*Tc/(sqr(mathematical::pi)*pow5(dp)*sqr(p.rho())*cc);
        f = mass*sqrt(mathematical::pi*s0/dt);
    }


    // To generate a cubic distribution (3 independent directions) :
    // const scalar sqrt2 = sqrt(2.0);
    // for (direction dir = 0; dir < vector::nComponents; dir++)
    // {
    //     const scalar x = rndGen_.sample01<scalar>();
    //     const scalar eta = sqrt2*erfInv(2*x - 1.0);
    //     value.Su()[dir] = f*eta;
    // }


    // To generate a spherical distribution:

    Random& rnd = this->owner().rndGen();

    const scalar theta = rnd.sample01<scalar>()*twoPi;
    const scalar u = 2*rnd.sample01<scalar>() - 1;

    const scalar a = sqrt(1 - sqr(u));
    const vector dir(a*cos(theta), a*sin(theta), u);

    value.Su() = f*mag(rnd.GaussNormal<scalar>())*dir;

    return value;
}


// ************************************************************************* //
